Metabolic Rate
Resting Metabolic Rate (RMR) and Basal Metabolic Rate (BMR) are the measures of resting energy expenditure in our body. Resting metabolic rate refers to the amount of energy used by the body in a given period of time when the body is in an inactive state. This energy is merely used to maintain the basic body functions like keeping heart beating, lungs breathing, and maintaining a normal body temperature. RMR measurements are usually taken after an overnight sleep.
Factors Affecting Metabolic Rate
Body functions are maintained by constant amount of energy expenditure. Factors like age, gender, height, weight, activity, race and others such as climate, smoking, and nutrient intake effect energy expenditure of our body and this in turn affect resting metabolic rate. When we skip meals, our metabolism decreases as the body burns fewer calories and stores excess fat resulting in weight gain. Therefore, it is very important to have small meals at regular intervals to maintain a stable metabolic rate.
Lean muscle mass burns more calories, and a high percentage of lean body weight results in a higher metabolic rate. Men are high on lean muscle mass and as a result have higher RMR than women. Tall people have more active metabolism and require higher calories. People born with a family history of slow metabolism have a higher tendency to gain weight. Adequate sleep is important to mobilize the carbohydrates and improve upon the calorie burning. A tired body has lower metabolic rate than a relaxed body.
Exercise and activity also raise our RMR from 100 to even upto 3000 calories per day.
Energy Balance = Energy Expended (exercise/activity) – Energy Intake (calories)
Our body requires a basic amount of energy to function every day, even when we’re sleeping. To perform body functions, our body needs energy in form of calories. Our resting metabolic rate is number of calories our body needs to just exist. Amount of energy expended when our body is in state of rest to sustain body functions is almost 70% to 75% of daily energy expenditure. Our daily activities account for about 20-30% of energy expenditure and the digestion process solely accounts for about 10% of daily energy expenditure.
Volume of our fat-free muscular mass is best predictor of RMR. RMR decreases with age. RMR normally ranges from 1,200 to 2,000 kcal/day (from 1,400-1,600 kcal/day in most people). Heavier people have higher RMR because they have more mass to support. Each pound of muscle burns to produce 6-7 kcal/day. Weight loss occurs only when our energy expenditure is greater than our caloric intake. RMR decreases on losing weight.
It is of prime importance to determine a person’s resting metabolic rate in order to design a weight loss program for that individual. Someone who is overweight has a higher RMR than a person who is lean. This is the reason why a person loses weight faster at the beginning of his weight losing regimen, gradually slowing down as he reaches his desired weight.
A person is not always at a state of rest, so the actual calories burned throughout the day will be higher than the RMR. The daily caloric intake should never go below the RMR to maintain a stable weight.
Going by individual body organs, our heart and kidneys have the highest resting metabolic rate (200 calories per pound), followed by brain (109 calories per pound) and liver (91 calories per pound). The contribution of skeletal muscle and fat to resting energy expenditure is smallest as compared to other organs.
